Improved photosynthesis by leaf nutrient content enhances water use efficiency in Juniperus tibetica along elevation gradients above 4000 m a.s.l.

Background
Leaf functional traits can influence the ability of plants to grow when facing stresses. Climate changes can impose fundamental impacts on plant growth, especially at high mountains. Yet little is known about relationships between leaf functional traits and elevations in tree species above 4000 m a.s.l.

Aims
Our objective was to investigate and compare the trend in water use efficiency (WUE) in the Tibetan juniper (Juniperus tibetica) along elevation gradients under different climate conditions, and by presenting evidence from leaf functional traits, to simultaneously clarify the underlying mechanisms.

Methods
We investigated various leaf functional traits, i.e. leaf carbon (δ13C) and oxygen (δ18O) isotopic composition, leaf N and P concentration and specific leaf area (SLA) in J. tibetica, a dominant tree species of the treeline, along elevation gradients at three study sites between 4150 and 4950 m a.s.l. in the Qinghai-Tibet Plateau.

Results
As elevation increased, leaf δ13C, used as a proxy for WUE, increased, whereas leaf δ18Odecreased in J. tibetica. Leaf Narea also increased with elevation.

Conclusions
We deduced that increasing WUE with elevation was due to enhanced photosynthetic capacity at all three study sites, and increased Narea may enhance photosynthesis and hence WUE.